Integrated circuits (ICs) and other electronic devices often include arrangements of interconnected field effect transistors (FETs), also called metal-oxide-semiconductor field effect transistors (MOSFETs), or simply MOS transistors or devices. A typical MOS transistor includes a gate electrode as a control electrode and spaced apart source and drain electrodes. A control voltage applied to the gate electrode controls the flow of current through a controllable conductive channel between the source and drain electrodes.
Power transistor devices are designed to be tolerant of the high currents and voltages that are present in some applications. Some power transistor devices are also designed to handle radio frequency (RF) signals, such as the devices used in wireless communications and other RF power amplifier applications. One type of RF power transistor device is a laterally diffused metal-oxide-semiconductor (LDMOS) transistor. In an LDMOS device, charge carriers drift through a drift space between a channel region and the drain electrode under the electric field arising from an operating voltage applied between the source and drain electrodes.
The high operating voltages between the source and drain electrodes of an LDMOS device may give rise to the generation of minority carriers through impact ionization. If a sufficient number of minority carriers are present in the channel region, the junction between the channel region and the source region of the LDMOS device can act as a base-emitter junction of a parasitic bipolar transistor. Destructive levels of current may occur in a condition referred to as “snapback,” if the parasitic bipolar transistor turns on.